Black hole
Black Holes A black hole as defined as being a massive object whose mass is so large that the graviational force it exerts prevents any object that enters a specific distance within it from escaping, except in the case of certain quantum mechanical phenomena. The specific distance from it's center, or it's singularity is known as it's event horizon. The term hole is really a misnomer as it is not actually a hole in space, merely a place of no return. A black hole is believed to be the end result of a supermassive star collapsing in upon itself. Evolution of a Black Hole Birth of Tragedy The universe is filled with a menagerie of different stars, ranging from medium stars such as ours, to ones significantly smaller and dimmer, to ones much larger and older. A star is basically a combination of two forces. The explosive nuclear force of fusion. Giving us light and heat, and the implosive force of gravity. Implosive in the sense that gravity is a force of attraction, it draws matter towards other bits of matter. A star is a delicate balance of both of these implosive and explosive forces. If a star were to have too great an explosive force in comparison to its implosive force, it would nova (explode). But if the star were to have a gravitational force that was stronger than its explosive force it would collapse upon itself. Depending on the mass of the star, a variety of things may happen. (Note, the following hypothetical scenarios involve stars which have the same circumference as our sun until they collapse. If the star has a larger circumference, more mass would be needed, if the circumference is smaller, then the opposite is true.) White Dwarfs If the star, is say slightly larger than our sun, only up to 1.4 times more massive though, when its nuclear fuel is exhausted and the explosive force decreases drastically, it would begin collapsing unto itself. But then it would suddenly halt. Thanks to the incredible repulsion forces of electrons known as electron degenerancy. The electrons in essence are very claustrophobic and spazz out when confined. As long as the mass is within 1.4 times that of our own sun's this holds true. At this point in time, the force of gravity is counter balanced by this force, as the star becomes what is known as a White Dwarf. Not this... But this... Neutron Star But if the star is between 1.5 solar masses (a form of measurement, it's a unit standing for the mass of one of our sun's) and 3 solar masses, something quite different happens. The electron degenerate force is overwhelmed by gravity and it is compressed into another type of star, a neutron star. At this point in time, the force of repulsion is coming not from the electrons, which are undergoing some strange quantum process of compression converting both the protons and electrons into even more neutrons. As it turns out, the repulsive nuclear force comes from the neutrons. And thus the fate of a black hole is avoided. Death... or is it? Then there's the final case. When a star is larger than all those masses, with a limited circumference, it has no choice but to collapse unto itself. It's mass is within 3 to 5 solar masses and so nothing can stop it from collapsing into a black hole. But what exactly happens here, is a mystery. A final note. Though there are a great deal of stars in the universe, most of the stars, while undergoing the process of collapse, they eject a great deal of matter. In so doing, they in effect avoid becoming black holes. An old latin proverb states "Nature abhors a vacuum." Anatomy of a Black Hole A black hole consists of several different parts, which generally are it's accretion disk, a singularity and an event horizon. Each component has it's own unique properties and is constituted of different things. (A black hole is not limited to just these parts, as shall be discussed later on.) The Accretion Disk The accretion disk is merely a cloud of matter outside of the black hole swirling inward. This matter, as it approaches the black hole reaches unfathomably large speeds, and most of it is actually deflected away from the event horizon. Black holes are borderline anorexic, they only consume 2% of the matter that they come in contact with. Thanks to the speed the matter reaches before the event horizon, it is deflected into 2 separate jets, both perpendicular to the accretion disk. These jets are a large source of magnetic radiation, and emit large amounts of X-rays, not within the visible spectrum. It is through this accretion disk that these black holes are indirectly detected, among other methods. The Event Horizon The event horizon is often symbolized by a pitch black circle, mainly because thats all that can be 'seen'. The even horizon is the point of no return for matter. After that, the force of gravity is so great, that not even light can escape it. But to say that a black hole does not generate radiation is not entirely true. For many years a black hole was considered to not generate radiation on it's own, mainly thanks to its extreme gravity. But, after the advent of quantum mechanics, a loop hole was found in that belief. Thanks to several bits of quantum phenomena all tied together under the title of Hawking Radiation, it was found out that they in fact radiate energy. Though this radiation of energy comes at a price. A black hole radiates infrared light, an almost infintesimal amount, but in so radiating it, it expends it's mass. After several million years, perhaps billion, a black hole will in essence evaporate. All this happening at the edges of the event horizon. Not just strange quantum effects happen here, but thanks to the immense gravity, we can experience time dilation, and other effects from General Relativity. (Note Hawking radiation is just a theory, but there is a great deal of building strength behind it.) The Singularity This would be the must confusing point of the black hole. It is where the mass goes, the stomach of the black hole. But currently there is no theory to explain what exactly is happing at this point, where all the mass of the star is believed to be compressed to about the planck legnth. General Relativity is a theory that specializes in the large, large masses, large distances. Where as Quantum Mechanics is a theory that describes matter when it has a very small mass and is very tiny. The mass at this point is quite large, but the distance is quite small. One can only hypothesize what is actually here. No 'naked singularity' (a singularity with no event horizon) has ever been seen in nature, and it is hypothesized that nature quite simply doesn't permit us to see them. For all we know, this could be past the event horizon... History Black holes have had a turbulent history, from their conception in 1783 when a star with a mass so large that light would be unable to escape it, was presented. This at the time was known as a Dark Star (tres cool name). No one payed much attention to it until Albert Einstein began his work on Relativity. Around that point in time he was contacted by Karl Schwarzschild who did brilliant work up until his death relating the mathematics surrounding black holes. Schwarzschild's work revolved around describing the geometric features of a black hole in non-eucledian space. About 5 years later in the 1920's now, Subrahmanyan Chandrasekhar presented brilliant work that argued against black holes. Using white dwarfs as his crux. He was overcome by a verbally abusive yet some how at the same time respectful Arthur Eddington. In the end, they were both right, and both wrong, all thanks to the proofs surrounding neutron stars. In essence, a star could possibly continue it's collapse if it's mass was large enough, but would be halted by the forces repelling the neutrons. Chandrasekhar argued that as a star died, and became cold, it would collapse. But it's collapse would be halted by the quantum phenomena of electron degenerancy. Eddington felt that even that would be unable to stop the star from eventually becoming a black hole and spent a great deal of time arguing with Chandrasekhar to the point at which Chandrasekhar was actually scarred (psychologically) and refused to speak in public about his ideas. This highly aggressive form of argument may have actually been Eddington's way of showing respect to a worthy adversary. In the late 1930's and early 1940's Oppenheimer put his weight behind black holes and came up with several theories surrounding them. Still, black holes weren't exactly proof positive. He theorized that past the event horizon we would see the star frozen forever in the process of collapse thanks to time dilation. Still many didn't believe this, convinced that since a star was not perfectly spherical, it could never collapse so perfectly into a singularity. It wasn't until Stephen Hawking managed to demonstrate that Black Holes are common place in Einsteinian physics (note, this was done in the 1960's, it took almost 200 years for black holes to be accepted) with his voodoo math. Shortly after Stephen Hawking proves the idea of black holes, the actual term is coined by John Wheeler. And still, we have no idea what's inside of them, but we've actually seen some and made a shocking discovery. As stated before, there's no real mathematical description suitable for what happens in there. As it turns out, the core of a galaxy is an ubermassive black hole. We are part of a black hole, not quite accretion disk by definition, but something much more. Quite incredible isn't it? There was an interesting proof behind this shown by radiotelescopes measuring the acceleration of bodies closer to the core of the galaxy as opposed to those on the outside. 'Math That We Won't Understand' I have the formula's here just for kicks. They're kinda beyond our simple high school level. First off we have a bit of Einsteinian equations, this describes the curvature of space around the black hole. where is a standard element of solid angle. The culmination of Schwarzschild's work can be found here The units here can be found on our reference tables. Except for what it equals, which would the Schwarzschild Radius. The density of the matter within the black hole is... In order to find the entropy of the actual black hole you would need this... And if you're ever in space and run into a black hole and are curious as to it's radius Say hello to E.T. for me. Thanks to these types of formula's Black holes are excluded from the regents, you can find the evidence in your regents physics book which never mentions black holes, not once! References http://en.wikipedia.org/wiki/Black_holes (For the mathy stuff) Thorne, Kip S. Black Holes & Time Warps. New York: W. W. Norton & Company Inc., 1994. 1-619. Barron's Regents Book. It had nothing, literally. 'nuff said. And lots of discovery channel specials that worked towards my edification on black holes Pictures acquired from: *www.eso.org (neutron star) *www.williams.edu (white dwarf) *ambassadors.net (mini me) *science.nasa.gov (event horizon) *www.roe.ac.uk (black hole) *www.llnl.gov (accretion disk) *www.und.nodak.edu (question mark) *my.opera.com (happy noodle boy, artwork originally by Johnen Vasquez) category:physics